Non-locking switch for filter monitoring

ABSTRACT

Commercially available filter-monitoring switches suffer from problems related to over sensitivity and reliability. Accordingly, the present inventors have devised, among other things, various embodiments of filter-monitoring switches and related components, subassemblies, methods, and systems. One exemplary filter-monitoring switch includes a diaphragm operably couple to move a conductive element back and forth between a pair of fixed terminals in response to pressure differences across the diaphragm. The conductive element is mounted to an insulative pin of substantially uniform width, and the terminals include leaf contacts that constantly engage the pin or the contacts throughout normal operation of the switch, thereby reducing flexure of the contacts and effectively providing a self-cleaning and self-healing electrical switch.

RELATED APPLICATION

The present application claims the benefit under 35 U.S.C. 119(e) ofU.S. Provisional Patent Application 60/648,169 which was filed on Jan.28, 2005 and which is incorporated herein by reference.

COPYRIGHT NOTICE AND PERMISSION

A portion of this patent document contains material subject to copyrightprotection. The copyright owner has no objection to the facsimilereproduction by anyone of the patent document or the patent disclosure,as it appears in the Patent and Trademark Office patent files orrecords, but otherwise reserves all copyrights whatsoever. The followingnotice applies to this document: Copyright © 2005 Engineered ProductsCompany, Inc.

TECHNICAL FIELD

Various embodiments of the present invention concern devices formonitoring fluid-filter performance, particularly devices thatincorporate an electrical switch responsive to a differential pressure.Some embodiments of the invention may also be used in otherapplications.

BACKGROUND

Many modern systems include air or liquid filters to ensure proper orreliable performance. For example, automobiles include air and fuelfilters to remove dirt and other particulates from the air and fuel thatare mixed and then ignited within their internal combustion engines. Asa consequence of their proper operation, these filters collectparticulates over time and increasingly restrict the flow of air or fuelinto engines. Eventually, the filters become more restrictive thandesirable and require replacement.

To facilitate timely filter replacement, automobiles and other systemssometimes include filter-monitoring devices, which monitor pressure orvacuum levels that result from fluid flow through associated filters.These devices are calibrated to detect when particular pressure orvacuum conditions occur and to respond to such occurrences in particularways. For example, some devices, referred to herein as filter-monitoringswitches, open or close an electrical switch, which is typically wiredto illuminate a warning light or to send a signal to an engine computerfor further processing.

The present inventors have recognized that commercially availablefilter-monitoring switches suffer from at least three problems. First,some filter-monitoring switches are overly sensitive to spiking orfluttering pressures and thus prematurely signal filter replacement orprovide a fluttering output signal that is difficult to process. Second,overly sensitive switches experience recurrent arcing between theirelectrical contacts that degrades performance, and often leads topremature failure of the switches. And, third, some switches allow dustand water intrusion that can also degrade performance and causefailures.

Accordingly, the present inventors have recognized a need to improveconventional filter-monitoring switches.

SUMMARY

To address this and/or other needs, the present inventors devised, amongother things, various embodiments of filter-monitoring switches andrelated components, subassemblies, methods, and systems. One exemplaryfilter-monitoring switch includes a diaphragm, and a switch defined by aconductor, and a pair of terminal contacts. In operation, the diaphragmflexes in response to differences in pressures on its opposing sides andcauses the conductor to move relative the pair of terminal contacts.Depending on initial position of the conductor and the differentialpressure, movement of the conductor can make or break contact with thepair of terminals.

In one exemplary system, the diaphragm separates a chamber into twoparts, one coupled to the atmosphere and the other to a fluid inlet ofan internal combustion engine. The fluid inlet receives filtered air orfuel from a corresponding filter. As the filter becomes dirty or cloggedwith particulates, it increasingly restricts fluid flow through theinlet and increases the differential pressure on the diaphragm,eventually forcing movement that either opens or closes the switch. Theswitch is coupled to an electric circuit, which operates an indicatorlamp or sends an electrical signal to a vehicle computer system.

In some embodiments, the portion of the chamber coupled to atmosphereincludes a vent hole, a dust cover, and a Teflon filter. The Teflonfilter, which is sandwiched between a region surrounding the vent holeand the dust cover, not only safeguards the switch from water and dustintrusion, but also dampens response of the switch to pressure changes.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a block diagram of an exemplary engine system 100 whichcorresponds to one or more embodiments of the invention.

FIG. 2A is a cross-sectional view of an exemplary filter-monitoringswitch 200, which corresponds to one or more embodiments of theinvention.

FIG. 2B is an exploded perspective view of filter-monitoring switch 200.

FIG. 2C is a perspective view of an exemplary push plate whichcorresponds to one or more embodiments of the invention.

FIG. 2D is a perspective view of an exemplary module 300 whichcorresponds to one or more embodiments of the invention.

FIG. 2E is a perspective view of an exemplary terminal which correspondsto one or more embodiments of the invention.

FIG. 3A is a cross-sectional view of an exemplary filter-monitoringswitch 400, which corresponds to one or more embodiments of theinvention.

FIG. 3B is an exploded perspective view of switch 400.

FIG. 3C is a perspective view of an exemplary dust cover whichcorresponds to one or more embodiments of the invention.

FIG. 4 is a cross-sectional view of an exemplary filtering monitoringdevice 400, which corresponds to one or more embodiments of theinvention.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENT(S)

This description, which incorporates the above-identified figures andappended claims, describes one or more specific inventive embodiments.These embodiments, offered not to limit but only to exemplify and teachone or more inventions, are shown and described in sufficient detail toenable those skilled in the art to implement or practice theinvention(s). The description may use terms, such as upper or lower inreference to specific features of various as embodiments; however,unless included in the claims, such terms are merely to aid correlatingthe drawings with the written description. Moreover, where appropriateto avoid obscuring the invention(s), the description may omit certaininformation known to those of skill in the art.

FIG. 1 shows a block diagram of an exemplary engine system 100 whichincorporates teachings of the present invention. System 100 includes anengine 110, a fuel filter 120, an air filter 130, filter-monitoringswitches 140 and 150, and monitoring circuitry 160 and 170.

Engine 110 includes an air inlet 111 and a fuel inlet 112 forrespectively channeling air and fuel into engine 110 for combustionaccording to known principles. In the exemplary embodiment, engine 110takes the form of an internal combustion engine; however, in someembodiments, engine 110 takes other forms.

Fuel filter 120 provides a filtered fuel flow 121 through fuel inlet 112to engine 110. In the exemplary embodiment, fuel filter 120 takes anyconvenient or desirable form.

Air filter 130, which is in fluid communication with air inlet 111,provides a filtered air flow 131 through inlet 111 to engine 110. In theexemplary embodiment, air filter 130 takes any convenient or desirableform.

Filter-monitoring switch 140, which is sized for operation as “airswitch” or filter-monitoring air switch, includes a chamber 141, acalibration spring 142, a diaphragm assembly 143, and a terminalassembly 144.

Chamber 141 includes an inlet portion 141A, and respective upper andlower chambers 141B and 141 C. Inlet portion 141 provides fluidcommunication between upper chamber 141B and air inlet 112. Upperchamber 141B, in the exemplary embodiment, snap fits onto lower chamber141B. Lower chamber 141C includes a breather hole 141D which allowsfluid communication between the lower chamber and ambient atmosphere.Hole 141D is covered with a dust cover 141E and a fluid filter 141F.Dust cover 141E sandwiches fluid filter 141F between an interior surfaceof the dust cover and a region surrounding hole 141D. In the exemplaryembodiment, fluid filter 141F consists essentially of a gas-permeable,water-repellant material, such as Porex IRM-0217 or XM-1484 (TeflonPTFE—Polytetrafluoroethylene). However, some embodiments form thematerial using other vinyl polymers or other materials made from themonomer tetrafluoroethylene. Still other embodiments use felt or otherporous filter media.

Calibration spring 142 fits between an upper interior surface of thechamber and diaphragm assembly 143, biasing response of the diaphragmassembly to differential pressures between the upper and lower chambers141B and 141C. Some embodiments may omit calibration spring 142.

Diaphragm assembly 143 includes a deflectable diaphragm 143A, and a pinassembly 143B. Diaphragm portion 143A, which includes a flexible andsubstantially fluid impervious membrane, provides a generallyfluid-tight seal between upper and lower chambers 141B and 141C.(‘Generally fluid-tight,’ as used herein, refers to a seal that has aleakage rate low enough to not interfere with the operation of thediaphragm and the filter-monitoring switch.) Diaphragm portion 143Adeflects or otherwise moves from a neutral position N to anotherposition F in response to a differential pressure between the upper andlower chamber portions, thereby moving pin assembly 143B up or downalong a central axis 140A.

Pin assembly 143B includes a non-conductive pin portion 143C and aconductive portion 143D. Non-conductive pen portion 143C extendsorthogonally away from the diaphragm portion 143A into lower chamber141C. Conductive portion 143D, which has substantially the same width orouter diameter as that of pen portion 143C, making it flush with thesurface of pin portion 143C. Conductive portion 143D is mounted at aposition on pin portion 143C to ensure contact with terminals 144A and144B of terminal assembly 144 when diaphragm portion 143A is in itsneutral (or relaxed state.) The exemplary embodiment forms conductiveportion 143D as a cylindrical bushing of hard gold plated brass thatencircles pin portion 143C.

Terminal assembly 144 (or switch assembly) includes terminals 144A and144B and a bias element 144C. Terminals 144A and 144B are spaced apart adistance Y, which is less than nominal width X of pin assembly 143B.Bias element 144C generally represents means for biasing terminals 144Aand 144B to apply a substantially constant force to the pin assembly asit moves between the terminals in response to differential pressuresbetween the upper and lower chambers. Terminals 144A and 144B areelectrically coupled to circuitry 150 via a two-terminal connector 151.

Circuitry 150 includes, in addition to connector 151, a warning lamp152, a battery 153, a warning lamp 154, and a two-terminal connector155. Warning lamp 152 and filter-monitoring switch 140 are coupled inseries across battery 153, enabling switch 140 to activate or deactivatethe lamp as diaphragm assembly 143 responds to differential pressurebetween upper and lower chambers 141B and 141C. (In some embodiments,the warning lamps are replaced with input port for a vehicle computingsystem, which includes a analog-to-digital converter.) Battery 153 isalso coupled across the series connection of warning lamp 154 andconnector 155, which itself is connected to filter-monitoring switch160.

Filter-monitoring switch 160, which not only operates warning lamp 154in a manner similar to filter-monitoring switch 140, but also has asimilar structure arrangement, includes a chamber 161, a calibrationspring 162, a diaphragm assembly 163, and a terminal assembly 164.Switch 160, however, is sized and constructed to operate as a “fuelswitch.” Additionally, in this exemplary embodiment, switch 160 is shownin a pressure configuration, with spring 162 positioned in a lowerchamber 161C, rather than upper chamber 161B to counteract relativehigher fluid pressures in upper chamber 161B. In contrast, switch 140 isshown in a vacuum configuration, with spring 142 positioned in upperchamber 141B to counterbalance the relatively higher atmosphericpressures in lower chamber 141C.

FIGS. 2A and 2B respectively show cross-sectional and perspectiveexploded views of an exemplary filter-monitoring switch 200. Switch 200includes a housing assembly 210, a diaphragm assembly 220, and a switchmodule 230.

Housing assembly 210, which includes a housing 212, a cap 214, afiltration system 216, and a collar 218. In the exemplary embodiment,all components of the housing assembly, except for filter 216B andcollar 218 are molded from Clariant Nylon 6/6 (13% Glass Filled.).Filter 216B is formed of Teflon PTFE, and collar 218 is formed ofaluminum, with edge rolled down after assembly of the switch.

More particularly, housing 212, which in the exemplary embodiment has agenerally cup-like structure, includes a fluid inlet 212A and a sidewall212B. The height of sidewall 212B is selected not only to permitmovement of diaphragm assembly 220, but also to prevent it fromtraveling too far during over-pressure situations. Housing 212 isattached to cap 214, for example via a snap fit, to form a chamber 213,having upper and lower chambers 213A and 213B analogous to chambers 141Band 141C in switch 140.

Cap 214, which is generally horn-shaped in the exemplary embodiment,includes a breather hole 214A, a stem portion 214B, and a rib portion214C. Breather hole 214A is in fluid communication with ambientatmosphere through filtration system 216.

Filtration system 216 includes a dust cover 216A and filter 216B, withthe dust cover adjacent an exterior portion of cap 214 sandwichingfilter 216B. Air can enter the dust cover, and consequently the lowerchamber, through one or more openings distributed in the sidewall of thecover.

Collar 218 encircles the interface between housing 212 and cap 214 toadd further integrity and aesthetic appeal to the switch. Collar 218includes upper and lower rolled edges 218A and 218B. Some embodimentsomit collar 218.

Diaphragm assembly 220, which provides a generally fluid tight sealbetween upper and lower chambers 213A and 213B, includes a diaphragm222, a retaining ring 224, and a push plate 226.

Diaphragm 222 includes an annular outer bead 222A and an inner annularbead 222B, which peripherally bound a convex annular portion 222C. Outerbead 222A is sandwiched between respective annular portion of the upperand lower chambers, more precisely housing 212 and cap 214. Innerannular bead 222B is sandwiched between retaining push plate 224 andretaining ring 226, which engage each other via a snap fit. Theexemplary embodiment forms diaphragm 222 from silicon or other suitablematerial.

Retaining ring 224 includes an annular trough 224A which seats a lowerportion of calibration spring 225. The spring can be selected tocalibrate the diaphragm so as not to deflect until a threshold pressure,or pressure difference is reached within the inner cavity. (Notably, thedesign of the diaphragm assembly is flexible in allowing in someswitches the calibration spring to be placed in the upper chamberbetween the housing and retaining ring, and in others to be placed inthe lower chamber between the cap and the push plate.) Retaining ring224 also secures and seals the diaphragm against an annular flangeportion 226A of push plate 226.

Push plate 226, which is also shown in FIG. 2C as being generally abell-shaped structure molded from Vydyne 22HSP Nylon, includes anannular wall portion 226B, a plate portion 226C, a pin portion 226D, andconductive bushing 226E. Annular wall portion 226B includes an upperridge 226BA which together with annular flange portion facilitate thesnap fit with retaining ring 226. Plate portion 226C is bounded byannular wall portion 226B, and positioned intermediate upper ridgeportion 226BA and annular flange portion 226A. Analogous to pin portion143B in FIG. 1, pin portion 226D extends orthogonally from a centralregion of plate portion 226C, with the lower end of the pin portionencircled by conductive bushing 226E. In one embodiment, conductivebushing is positioned closer to the end of the pin to define the switchas a normally open switch, and in another it is positioned further fromthe end of the pin to define a normally closed contact. The majority ofthe length of pin portion 226D extends through a guide hole 236C ofterminal module 230.

Terminal module 230, shown also in FIGS. 2D and 2E, and 2F, includes aterminal assembly 234 and upper and lower portions 236 and 238. Terminalassembly 234 includes a pair of substantially identical non-contactingterminals 234A and 234B. Shown best in FIG. 2D, terminal 234B includes aterminal pin 234BA, a terminal pad 234BB, and a leaf contact 234BC.Terminal pin 234BA, which is sized to engage or mate with a femaleconnector (not shown), is formed of half-hardened brass and tin plated.Substantially covering terminal pad 234BB, leaf contact 234BC is formedof beryllium-copper and includes a spring portion 234BD. Insert-moldedaround terminal assembly 234 are upper and lower module portions 236 and238.

In the exemplary embodiment, module portion 236 and 238 are formed ofVydyne Nylon 6/6 22 HSP. Upper portion 236 includes guide hole 236A andmodule support 236B. Lower portion 238 has a sleeve portion 236A with anotch 236B, with the sleeve portion extending from the opposite side ofthe module support as upper portion 236A. Notch 236 extends along thelength of the sleeve portion and engages with rib 214C in the stemportion of cap 214 to ensure alignment of guide hole 236A with centralaxis 202A and pin 226D and to provide additional rigidity. The modulesupport is sealed around the prongs (terminals) to prevent contaminantsfrom entering into the lower chamber.

In the exemplary embodiment, the terminal-module-to-cap interface is notfluid tight; however, a suitable connector adapted to fit within thestem portion of cap 214 can seal this portion of the cap and restrictbreathing of the lower chamber to filtration system 216. The modulestructure is also attached to the cap, and the module structure does notmove with respect to the housing assembly.

FIGS. 3A, 3B, and 3C respectively show cross-sectional and perspectiveexploded views of an exemplary filter-monitoring switch 300, which isstructurally and functionally similar to switch 200, with the exceptionthat switch 300 is intended for use in smaller spaces and greaterdifferential pressures than switch 200 and includes a different dustcover 316B and a different diaphragm assembly 320.

Filtration system 316 includes a dust cover 316A and a filter 316B, withthe dust cover and an adjacent exterior portion of cap 314 sandwichingfilter 316B. FIG. 3C, an underside perspective view of dust cover 316A,reveals interleaved ribs 316BA and 316BB and openings 316BC. Interleavedribs 316BA provide a maze-type barrier between openings 316BC and acavity 316BD that receives an upper portion of filter 316B.

Diaphragm assembly 320, which provides a generally fluid tight sealbetween upper and lower chambers 213A and 213B, includes a diaphragm322, a retaining ring 324, and a push plate 326.

Retaining ring 324, which is generally dome shaped, includes an annularflange 324A which seats a lower portion of the calibration spring andupper hole 324B. Retaining ring 324 also secures and seals the diaphragmagainst an annular flange portion 326A of push plate 326. Push plate 326is also dome shaped and includes an annular wall portion 326B, a plateportion 326C, a pin portion 326D, and conductive bushing 326E. Annularwall portion 326B includes upper snaps 326BA and a lower flange 326BBwhich respectively engage upper hole 324A in a snap fit arrangement,thereby securely sandwiching an inner bead of diaphragm 322 between thelower flanges of the retainer ring and the push plate. Pin portion 326Dextends orthogonally from a central region of plate portion 326C, withthe lower end of the pin portion encircled by conductive bushing 326E.

FIG. 4 shows a cross-sectional view of an alternative push plate 400,which may be substituted for the push plates of switches 140, 200, and300 to reconfigure those switches as variable pressure sensors. Pushplate 400, which is shown engaged with terminal module 230, includes apin portion 410 which extends orthogonally from a central region ofplate portion 226C, with the pin covered by a U-shaped resistivestructure 412 that leaves a portion of the insulative pin exposed. Asthe push plate structure is moved up and down relative to the leafcontacts, the resistive structure and the leaf contacts are in contactand the length of the resistive material that conducts a current changesin proportion to the displacement of the push plate, thereby providing acurrent or voltage that varies in a predictable or substantially linearfashion. The majority of the length of pin portion 410 extends throughguide hole 238C of terminal module 230.

Other embodiments based on this variable-resistance principle distributea plurality of spaced-apart conductive segments or portions along thepin. As the pin moves through its range of motion, different conductiveportions can contact the leaf assemblies. The different conductivesegments can be selected to have different resistances. Thus, as the pintravels through its range of motion, the different resistances modulatethe electrical signal passed between the leaf assemblies, effectivelyencoding the electrical signal with a measure of the diaphragmdisplacement, which in turn can be appropriately translated into adifferential pressure across the diaphragm.

The switch can be configured for use in a pressure, vacuum, ordifferential pressure mode. In addition, the switch can be configured tobe normally open or closed, or in “closed but variable resistance mode,”or the like. In one example, the operating range of switch where thefiltered fluid is air is between 13 to 30 inches of water. In anotherexample, the operating range of the switch where the filtered fluid is aliquid is typically between 3 to 13 inches of mercury. Othercalibrations are possible.

ADVANTAGES OF VARIOUS EMBODIMENTS

Various embodiments of the invention are believed to provide one or moreof the following advantages. For examples, some embodiments exhibitimproved damping characteristics in response to pressure spikes andpulsing that can lead to premature signaling and fluctuating signals.Damping is achieved in part by using a large deflectable diaphragm and alarge inner cavity volume. These two properties slow the response timeand minimize or reduce the force-to-friction ratio in the switches. Thelarge size and calibration spring prevent the switch from moving untilthe pressure gradient is close to the selected level. Variousembodiments has also shown an ability to function properely intemperature extremes (between −40 and 230 degrees F) and under vibration(between 20 to 200 Hz and 4 g).

Some embodiments are less likely to experience intrusion of dust andwater or other contaminants that could otherwise interfere with normaloperation. The housing assembly in one or more of the embodimentsincludes three components—the housing, the cap, and the dust cover,which collectively or individually reduce the amount of liquid or debrisintrusion. The tortuous or maze-like channels dissipate the energy ofany stream of contaminants. Drain holes are included to vent or removecontaminants. The use of obstructions, tortuous channels absorb anddisperse the energy of potentially intrusive fluid streams, and drainageholes allow contaminants to drain away. Additionally, the smallwater-repellant filter provides an additional barrier againstcontaminants.

Some embodiments may also provide additional benefits. For example someembodiments are relatively insensitive to switch orientation as a resultof the light weight of the moving switch components. Some embodimentshave a relatively low and substantially constant switch-contact force,which results in reduced hysterisis. Moreover, the wiping action of thepush-plate pin against the leaf contacts creates a self-cleaning,self-healing switch.

CONCLUSION

In furtherance of the art, the present inventors have presented variousfilter-monitoring devices, components and related systems. The foregoingdescription and examples have been given for clarity of understandingonly. Those skilled in the art will recognize that many changes can bemade in the described examples without departing from the scope of thisdisclosure. Accordingly, the appropriate scope of this disclosureextends beyond the described examples.

1. A filter-monitoring switch comprising: first and second contacts forconnection to an electric circuit; a conductive member for electricallycoupling the first contact to the second contact; and a diaphragmcoupled to move the conductive member.
 2. The filter-monitoring switchof claim 1 further comprising: a push plate coupled to the diaphragm andhaving a central pin coupled to the conductive member.
 3. The switch ofclaim 2, further comprising a guide structure having a hole throughwhich the central pin extends, the guide structure fixed relative to thefirst and second contacts to guide movement of the central pin along anaxis between the first and second contacts.
 4. The switch of claim 2,wherein the conductive member is cylindrical and encircles a portion ofthe central pin.
 5. The switch of claim 1, wherein further comprisingfirst and second terminals that are electrically and mechanicallycoupled respectively to the first and second contacts; and a terminalsupport structure that is insert-molded around the first and secondterminals.
 6. The switch of claim 3, wherein the terminal supportstructure includes a sleeve around the first and second terminals, withthe shroud including a notch generally parallel to the first and secondterminal.
 7. The switch of claim 1, wherein each of the first and secondcontacts includes leaf contact biased toward the conductive member. 8.The switch of claim 1, further comprising a Teflon filter and a cover.9. A method of operating a filter-monitoring switch, the methodcomprising: electrically coupling first and second contacts by moving aconductor along an axis between the first and second contacts inresponse to a differential pressure condition.
 10. The method of claim9, wherein moving the conductor along the axis comprises flexing adiaphragm that is mechanically coupled to the conductor.